mash: Replace ShelfItemDelegate::CanPin with ShelfItem::pinned_by_policy.

ash/common/shelf/shelf_item_types.h

Index: ash/common/shelf/shelf_item_types.h
diff --git a/ash/common/shelf/shelf_item_types.h b/ash/common/shelf/shelf_item_types.h
index 386e979b931f46ac27994b90f81574f6882dbde2..998f33beddba4eae25a0096b7ba3200dc742c1ee 100644
--- a/ash/common/shelf/shelf_item_types.h
+++ b/ash/common/shelf/shelf_item_types.h
@@ -75,6 +75,9 @@ struct ASH_EXPORT ShelfItem {
 
   // Whether the tooltip should be shown on hover; generally true.
   bool shows_tooltip = true;
+
+  // Whether the item is pinned by a policy preference (ie. user cannot un-pin).
+  bool pinned_by_policy = false;
 };
 
 typedef std::vector<ShelfItem> ShelfItems;